<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <input type="text">
  <script>
    let input = document.getElementsByTagName('input')
    // 修改input的type属性 为一个按钮
    input[0].type = 'button'
    input[0].value = '我是一个按钮'
  </script>
</body>

</html>